stratosphere vs troposphere

stratosphere

noun
  • The region of the uppermost atmosphere where temperature increases along with the altitude due to the absorption of solar ultraviolet radiation by ozone. The stratosphere extends from the tropopause (10–15 kilometers) to approximately 50 kilometers, where it is succeeded by the mesosphere. 

troposphere

noun
  • The lower levels of the atmosphere extending from the surface of the Earth or another celestial body up to the tropopause. It is characterized by convective air movements and a large vertical temperature change. 

How often have the words stratosphere and troposphere occurred in a corpus of books? (source: Google Ngram Viewer )